The invention relates to a method of electrolytically metallising or etching material.
The economic operation of electrolytic metallising and etching methods essentially depends on the maximum current density at which an industrially useful treatment result may still be obtained. The maximum current density is above all dependent on the speed at which fresh treatment agent (electrolyte solution) can reach the surface of the material to be treated. During electrolytic metallisation, the precipitated metal ions are consumed in the direct vicinity of the material for treatment. This reduces the metallising speed, and the process decelerates. The same also applies to other electrolytic treatment methods, for example electrolytic etching.
In order to provide assistance here, flesh treatment solution can be supplied continuously trough flow tubes which in electrolytic metallisation are disposed between the anode and the material for treatment (cathode), on to the surface of the material for treatment. This procedure however is subject to certain fluidic limits; the exchange of liquid in the direct vicinity of the surface of the material for treatment (diffusion layer) may only be increased to a restricted degree. Apart from this, such a procedure is disadvantageous, as the flow tubes disposed between the anodes and the material for treatment screen the electrical field between the anodes and cathodes, so that metal is irregularly deposited on the material. This disadvantage is particularly serious when the space between the flow tubes and the surface of the material is small. On the other hand, for fluidic reasons a small space between the flow tubes and the material surface would be preferable, in order to achieve controlled flow direction and the highest possible current density. In this case high current densities would occur at some points on the surface of the material, so that the additives conventionally included in electrolytic metallising baths would become oxidised.
Plate-shaped material for treatment, particularly printed circuit boards, is preferably processed in horizontal treatment installations.
The material is grasped in a horizontal position and passed through the installation in a horizontal direction, thus being electrolytically treated. In such installations, rollers are normally used for transporting and guiding the material. These also are located in the area between anode and cathode. Particularly in the case of extremely thin films, guide members are also necessary in order to transport them efficiently, in order to prevent the films from slipping off the transport track and becoming wound around the transport rollers. Such constructional members, like the transport rollers mentioned, also hinder the current flow between the anode and the material for treatment.
Soluble anodes, produced from the metal to be precipitated, are normally used for electrolytic metallisation. Their positioning inside the metallising installation and their normal shape and size give rise to considerable difficulties in finding simple constructive solution to the named problems. When using insoluble anodes, there is on the other hand the possibility in horizontal installations of making these in a longitudinally-extended form, and of disposing them in such a way that the screening actions described do not occur. For example, in such arrangements, in repeated sequences of adjacent insoluble anodes, at least one flow tube may be disposed for supplying fresh treatment agent to the surface of the material, and to transport rollers. The positioning of these individual members is so selected that the material s moved slowly past them during the metallising process. The length of such an installation is determined by the geometrical dimensions of the three members, their necessary spacing apart from one another, and by their overall number. Such treatment installations are therefore extremely long and relatively expensive.